Fluidic axis position sensor for rotating mass

ABSTRACT

A fluidic axis position sensor is disclosed wherein the axis of rotation of a rotating mass may be determined by sensing irregularities on the surface of the rotating mass. The surface irregularities induce pressure changes in the ambient fluid which may then be sensed. The specific embodiment disclosed relates to a gyroscopic rotor formed by joining hemispheres of differing diameters. Upon rotation about an axis not having as an equator the discontinuity formed by the joint, the discontinuity induces pressure variations which are sensed by fluidic pickoffs spaced about the rotating mass. The output of each pickoff is a pulse width modulated signal whose duty cycle is used to determine the position of the axis of rotation of the mass.

United States Patent Ringwall [451 June 27, 1972 [54] FLUIDIC AXISPOSITION SENSOR FOR ROTATING MASS Primary Examiner-Manuel A. AntonakasAttorney-Frank L. Neuhauser, Oscar B. Waddell, Joseph B. 1 lnvemofl zScone, Forman, David M. Schiller and Arthur E. Foumier 73 Assi nee:General Electric Com an I 1 g p y 57 ABSTRACT [22] Filed: Feb. 18, 1970A flllldlC axis position sensor is disclosed wherein the axis of 1 PPN03 12,241 rotation of a rotating mass may be determined by sensingirregularities on the surface of the rotating mass. The surfaceirregularities induce pressure changes in the ambient fluid E 2 SI.which y then be sensed. The Specific embodiment disclosed 58 1 Fieid 573/515 relates to a gyroscopic rotor formed by joining hemispheres ofdifiering diameters. Upon rotation about an axis not having as anequator the discontinuity formed by the joint, the discon- [56]References Cited tinuity induces pressure variations which are sensed byfluidic UNITED STATES PATENTS pickoffs spaced about the rotating mass.The output of each pickoff is a pulse width modulated signal whose dutycycle is 3,267,747 8/1966 Paine ..74/5.6 X used to determine thcposition f the axis f rotation f the 3,311,987 4/1967 Blazek ..74/5.6 Xmam 3,362,233 1/1968 Posingies ..74/5.6 3,528,300 9/1970 Paine ..74/5.77 Claims, 6 Drawing Figures FLUIDIC AXIS POSITION SENSOR FOR ROTATINGMASS This invention relates to a sensor for determining the position ofthe axis of rotation of a rotating mass. More particularly it relates toasystem utilizing fluidic pickoffs for determining the position of theaxis of rotation of a gyroscopic rotor. 1

Fluidic pickoff systems for the purpose have, up to now, a ratherrestricted angular range over which they operate, typically :10". Othertypes of sensing schemes, non-fluidic, are encumbered by additionalequipment needed to convert the sensed signal into a useful output. Forexample, where optical sensors have been utilized, a source of light isnecessary, along with the attendant power supply, mirrors, photocells,etc. Further, it is generally necessary to utilize a pulse shaper forthe output of the photocells to obtain a uniform pulse.

In view; of the above, it is an object of this invention to provide anaxis of rotation position locator utilizing fluidic pickoffs and capableof operating over a wide angular range.

It is a further object of the presentinvention to provide an axis ofrotation position sensor utilizing fluidic pickoffs whose output signalhas sufficient definition to be utilized directly, without the use ofinterface or conversion equipment.

Another object of the present invention is to provide an axis ofrotation position sensor utilizing fluidic pickoffs whose output islinear over a large portion of its operating range.

Yet a further object of the present invention is to provide an axis ofrotation position sensor utilizing fluidic pickoffs and exertingnegligible torques on the rotating mass whose axis of rotation is beingsensed.

The foregoing objects are achieved in the present invention whereinthere is provided a. rotating mass, for example a sphericalgyroscopic'rotor, having an irregularity thereon, for example adiscontinuity along any great circle not an equator. Such adiscontinuity can be obtained by joining hemispheres of slightlydifferent diameters. Fluidic pickoffs placed around and adjacent to therotating mass sense the pressure variations induced by the surfaceirregularities on the mass. If the mass is the above-noted sphere, theoutput of the sensors comprises pulse width modulated waves whose dutycycle, i.e., the per cent ON" time of the period is indicative of theposition of the axis of rotation.

In some applications, the pulse widthmodulated output may be utilizeddirectly. For example, where the rotating mass is a gyroscopic rotor ina missile guidance system, the pulse width modulated output signals canbe amplified and used to directly modulate the steering thrusters of themissile.

A more detailed understanding of the present invention may be obtainedby considering the following description in conjunction with theattached drawings in which:

FIG. 1 illustrates one position of the rotating mass modified inaccordance with the present invention.

FIG. 2 illustrates the output waveform from one of the fluidic pickoffs.

FIG. 3 illustrates a second position of the rotating mass modified inaccordance with the present invention.

FIG. 4 illustrates the output waveform from one of the fluidic pickoffslocated adjacent to the rotating mass.

FIG. 5 illustrates another position of the rotating mass modified inaccordance with the present invention.

FIG; 6 illustrates the output waveform from a fluidic pickoff positionadjacent the rotating mass.

In FIG. 1 there is illustrated a rotating mass 10 having the particularform of a sphere comprising a first hemisphere portion I1 and a secondhemisphereportion 12 joined together along a great circle 13. As shownin FIG. 1, the spherical mass 10 rotates in an ambient fluid about itsaxis of rotation 14 and has defined around it yaw, pitch, and roll axesl6, l7, and 18, respectively. It is understood, of course, that thesenames are used in their ordinary sense, i.e., they refer to the threemutuallyv perpendicular axes used to define three dimensional snace. Theaxes chosen are for convenience only since nonorthogonal axes whileusable, would increase the calculations necessary for determining theposition of the axis of rotation of the spherical mass. As illustratedin FIG. 1, the axis of rotation 14 and the roll axis 18 are colinear,the spherical mass 10 has an equator 15 as the great circleperpendicular to the axis of rotation, and the great circle defining thejoint between the hemispheres I3 is inclined at an angle )3 to theequator I5. In the example given in FIG. 1 of a particular position forthe axis of rotation, fluidic pickoffs 16b and 17b are positionedadjacent to the spherical mass along the yaw and pitch axes,respectively, and sense the pressure changes induced by the change inradius of the spherical mass. The gap between the fluidic pickoff andthe rotating mass controls the pressure level sensed by the fluidicpickoff. A large gap induces a low level signal and a small gap inducesa high level signal. With the positioning as illustrated in FIG. 1, boththe pitch and yaw axis pickoffs sense equal duration high level and lowlevel signals. The output waveform from one of these fluidic pickoffs,for example the pitch axis pickoff, is illustrated in FIG. 2 by thecurve 21. As can be seen from FIG. 2, the curve 21 has a 50 percent dutycycle, that is, the high level signal exists for one-half the period andthe low level signal exists for the other half. Thus a 50 percent dutycycle signal from both the fluidic pickoffs would indicate that arotating spherical mass 10 has its axis of rotation along thearbitrarily defined roll axis.

In FIG. 3 there is illustrated a rotating spherical mass having its axisof rotation displaced an angle it in the plane containing the roll andyaw axes, that is, the axis of rotation is rotated about the pitch axis.In so doing, the fluidic pickoff along the pitch axis 17 no longersenses the pressure variations along the great circle; rather, it sensesthe pressure variations along a particular latitude illustrated bydotted line 19. The amount of latitude displacement is, of course, thesame as the angular rotation of the axis of rotation about the pitchaxis. When the fluidic pickoff along the pitch axis 17 is so displaced,the high level and low level output signals will no longer be of equalduration; rather, as illustrated in FIG. 4, the low level pressuresignal will be much shorter than the high level pressure signal sincemuch less of the low level pressure area is passing under the fluidicpickoff.

In FIG. 4 there is illustrated the output signal from the fluidicpickoff along the pitch axis 17. As can be seen from curve 22, the lowlevel signal has been shortened. The output signal of the yaw axisfluidic pickoff will be the same as that illustrated on curve 21 in FIG.2. This is because the yaw axis fluidic pickoff is still sensing thepressure variations along a great circle. If the axis of rotation hadbeen displaced out of the roll-pitch plane, then there would also be avariation in the duty cycle of the output signal from the yaw axispickoff.

FIG. 5 illustrates another position of the rotating mass 10 in which theaxis of rotation has been displaced in the opposite direction in theroll-pitch plane from that illustrated in FIG. 3. As can be seen fromFIG. 5 the pitch axis fluidic pickoff 17b is now displaced in theopposite direction and senses the pressure variations along a degree oflatitude in which the low level pressure areas are much greater than thehigh level pressure areas. The output signal from the pitch axis fluidicpickoff is illustrated in FIG. 6 by the curve 23. As can be seen fromthe curve 23, the high level signal duration has been greatly reducedand the duty cycle of the output waveform is much lower than that ofeither FIGS. 2 or 4. Again, as with FIG. 3, the yaw axis fluidic pickoff16b will continue to sense equal duration high and low level pressuresdue to the fact that is is still sensing pressure variations along agreat circle. If the axis of rotation 14 had been displaced out of theroll-pitch plane, then the duty cycle of the signal sensed by the yawaxis fluidic pickoff would also be changed.

For each fluidic pickoff output signal the ratio of the low level signalduration (t) to the period of rotation (T) of the sphere is given by thefollowing equation, from which the axis of rotation position may becalculated by any suitable means:

Where 1) is the spin axis displacement relative to the arbitrarilydesignated roll axis position, and

[3 is the angle of inclination between the equator and the great circledefining the discontinuity on the surface of the rotating mass.

Thus, it can be seen there has been provided an axis of rotationposition sensor utilizing fluidic pickoffs capable of operation over awide range of angular displacement. Where the rotating spherical mass isa gyroscopic rotor, the system of the present invention can be utilizedas a means of guiding a vehicle by monitoring the changes in directionwith the fluidic pickoffs. In certain applications such as missilesteering, the pulse width modulated signal obtained by the fluidicpickoffs can be amplified and used directly to modulate the steeringthrusters of the missile. This eliminates the need for including pulsewidth modulation circuits between conventional gyroscopic pickoffs andthe steering thrusters.

While a specific embodiment of the present invention has been disclosed,it will be obvious to those of ordinary skill in the art that variousmodifications can be made without departing from the spirit and scope ofthe present invention. For example, in a guidance system more than onerotating spherical mass may be utilized or more than two axial pickoffscan be used with a single spherical mass or a combination of these twocan be used thereby extending useful operating range of the over-allguidance system.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A fluidic axis of rotation position sensor comprising an ambientfluid,

a mass rotating about an axis of rotation in said ambient fluid,

said mass-comprisin g a first portion having a first radius and a secondportion having a radius greater than said first radius of said firstportion,

a discontinuity on the surface of said mass created by the differingradii of said first and second portions of said rotating mass, and

at lease two, coplanar, mutually perpendicular, fluidic pickoffsadjacent said rotating mass whereby said pickoffs sense pressurevariations in said ambient fluid caused by said discontinuity from whichthe position of said axis of rotation may be determined.

2. A fluidic axis of rotation position sensor as set forth in claim 1wherein said rotating mass is spherical.

3. A fluidic axis of rotation position sensor as set forth in claim 2wherein said discontinuity is along a great circle on said sphericalmass.

4. A fluidic axis of rotation position sensor comprising an ambientfluid,

a spherical mass rotating about an axis of rotation in said ambientfluid,

said spherical mass comprising two hemispheres of different radii joinedtogether,

a discontinuity on the surface of said spherical mass, and

at least two, coplanar, mutually perpendicular fluid pickoffs adjacentsaid rotating spherical mass whereby said pickoffs sense pressurevariations in said ambient fluid caused by said discontinuity from whichthe position of said axis of rotation may be determined.

5. A fluidic axis of rotation position sensor as set forth in claim 4wherein the portion of the spherical mass of smaller radius induces alow level output signal and the portion of the spherical mass of largerradius induces a higher level output signal and wherein the ratio of lowlevel signal duration (1), to the period of rotation (T) is given by:

where 4) is the axis of rotation displacement relative to an arbitraryzero position and [3 is the angle of inclination between the equator andthe great circle defining the discontinuity on the sphere.

6. A fluidic axis of rotation position sensor as set forth in claim 5wherein said spherical mass acts as a gyroscopic rotor and furthercomprising control means directly activated by said output signalswhereby a vehicle containing said gyroscopic rotor can be guided.

7. A fluidic axis of rotation position sensor as set forth in claim 5further including means for calculating 4) from said ratio.

1. A fluidic axis of rotation position sensor comprising an ambientfluid, a mass rotating about an axis of rotation in said ambient fluid,said mass comprising a first portion having a first radius and a secondportion having a radius greater than said first radius of said firstportion, a discontinuity on the surface of said mass created by thediffering radii of said first and second portions of saiD rotating mass,and at lease two, coplanar, mutually perpendicular, fluidic pickoffsadjacent said rotating mass whereby said pickoffs sense pressurevariations in said ambient fluid caused by said discontinuity from whichthe position of said axis of rotation may be determined.
 2. A fluidicaxis of rotation position sensor as set forth in claim 1 wherein saidrotating mass is spherical.
 3. A fluidic axis of rotation positionsensor as set forth in claim 2 wherein said discontinuity is along agreat circle on said spherical mass.
 4. A fluidic axis of rotationposition sensor comprising an ambient fluid, a spherical mass rotatingabout an axis of rotation in said ambient fluid, said spherical masscomprising two hemispheres of different radii joined together, adiscontinuity on the surface of said spherical mass, and at least two,coplanar, mutually perpendicular fluid pickoffs adjacent said rotatingspherical mass whereby said pickoffs sense pressure variations in saidambient fluid caused by said discontinuity from which the position ofsaid axis of rotation may be determined.
 5. A fluidic axis of rotationposition sensor as set forth in claim 4 wherein the portion of thespherical mass of smaller radius induces a low level output signal andthe portion of the spherical mass of larger radius induces a higherlevel output signal and wherein the ratio of low level signal duration(t), to the period of rotation (T) is given by: where phi is the axis ofrotation displacement relative to an arbitrary zero position and Beta isthe angle of inclination between the equator and the great circledefining the discontinuity on the sphere.
 6. A fluidic axis of rotationposition sensor as set forth in claim 5 wherein said spherical mass actsas a gyroscopic rotor and further comprising control means directlyactivated by said output signals whereby a vehicle containing saidgyroscopic rotor can be guided.
 7. A fluidic axis of rotation positionsensor as set forth in claim 5 further including means for calculatingphi from said ratio.